There has been proposed in the above mentioned U.S. Pat. No. 4,409,134 a semiconductor device formed using semi-amorphous semiconductor.
The semi-amorphous semiconductor herein mentioned is defined as a semiconductor which is formed of a mixture of a microcrystalline semiconductor and a non-crystalline semi-conductor and in which the mixture doped with a dangling bond neutralizer and the microcrystalline semiconductor has a lattice strain.
In the semiconductor device using the semi-amorphous semiconductor, the semi-amorphous semiconductor formed in the shape of a layer provides a large optical absorption coefficient as compared with a single crystal semiconductor. Accordingly, with a semi-amorphous semiconductor layer of sufficiently smaller thickness than the layer-shaped single crystal semiconductor of the semiconductor device using the single crystal semiconductor, it is possible to achieve a higher photoelectric conversion efficiency than that obtainable with the single crystal semiconductor device.
Further, in the semi-amorphous semiconductor device, the semi-amorphous semiconductor provides a high degree of photoconductivity, a high degree of dark-conductivity, a high impurity ionization rate and a large diffusion length of minority carriers as compared with an amorphous or poly-crystalline semiconductor. This means that the semi-amorphous semiconductor device achieves a higher decree of photoelectric conversion efficiency than an amorphous or polycrystalline semiconductor device.
Accordingly, the semi-amorphous semiconductor device is preferable as a semiconductor photoelectric conversion device.
In the foregoing semi-amorphous semiconductor device, however, the number of recombination centers contained in the semi-amorphous semiconductor is as large as about 1017 to 1019/cm3. Owing to such a large number of recombination centers, the diffusion length of the minority carriers in the semi-amorphous semiconductor is not set to a desirable value of about 1 to 50 μm which is intermediate between 300 Å which is the diffusion length of the minority carriers in an amorphous semiconductor and 103 μm which is the diffusion length of the minority carriers in a single crystal semiconductor. Therefore, according to the foregoing semiconductor technology, the semi-amorphous semiconductor device has a photoelectric conversion efficiency as low as only about 2 to 4%.
Further, there has been proposed, as the semiconductor device using the semi-amorphous semiconductor, a semiconductor device which has a plurality of electrically isolated semiconductor elements.
In such a semiconductor device, however, the structure for isolating the plurality of semiconductor elements inevitably occupies an appreciably large area relative to the overall area of the device. Therefore, this semiconductor device is low in integration density. In addition, the structure for isolating the plurality of semiconductor elements is inevitably complex. Therefore, the semi-conductor device of this type cannot be obtained with ease and at low cost.